Three investigators (Drs. McKay, Weis and Kornberg) are requesting resources to upgrade a ten-year-old multiwire area detector that is used for large-molecule x-ray crystallography. The crystallographic systems currently under study include (i) RNA polymerase in functionally relevant complexes with RNA, DNA and transcription factors; (ii) catalytic RNAs, including the hammerhead and hepatitis delta virus ribozymes and the "leadzyme"; (iii) molecular chaperones, including the 70 kDa heat shock protein family, the HslUV "chaperone-directed proteolysis" system, and DEAH-box RNA chaperones/helicases; (iv) C-type cell surface and host defense recognition lectins; (v) catenins and cadherins; and (vi) vesicular fusion proteins. This data collection system will also be used by Dr. Chris Garcia, a new faculty member in the Department of Microbiology and Immunology, when he arrives. The upgraded system will be used both for measuring complete datasets on crystals in-house and for screening crystals in preparation for data collection at synchrotrons.